limit switch current /diode

Discussion in 'The Projects Forum' started by jalt, Dec 24, 2015.

  1. jalt

    Thread Starter New Member

    Dec 19, 2015
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    I am thinking about hooking up limit switches to a linear actuator. Power requirements of a Warner Linear Actuator is 12 V DC 25 amp . My question is do the limit switches need to be able to carry 25 amps of 12 volt dc system ( going off the specifications linear actuator ) ? And what about the diode size /volts /amps ? Do diodes have to be able to carry a greater voltage value like 35 amps. Newbie here ! The link is a wire diagram of what I want to do. Any help would with this would be greatly appreciated.


    https://www.firgelliauto.com/products/external-limit-switch-kit-for-actuators
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,986
    3,226
    The limit switches do have to carry the actuator current.

    But I don't understand the diode connection. :confused:
    I assume the diode is for transient suppression but it won't do anything if it's connected across the limit contacts as stated in the connection diagram (unless it's a transient suppression diode).

    Assuming you want to reverse the polarity to the actuator to reverse its direction then you can use 4 standard diodes as shown below to suppress any inductive transients from the actuator.

    The diode only has to momentarily carry the actuator current during the transient so the diode surge rating just needs to be greater than the actuator current. Thus a 1N400x (x= 1-9) with a 30A surge rating should work fine.

    upload_2015-12-24_17-4-44.png
     
  3. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    If you can't find a limit switch that can carry 25 amps, we can fix that with a relay or a mosfet.;)
     
  4. jalt

    Thread Starter New Member

    Dec 19, 2015
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    0
    I am new to all this so "I could be very wrong". I was thinking the diode was to control direction of current only. Using DPDT switch in reversing the actuator direction. (and current). The diode will not allow current to feed back the wrong way. Being there are two limit switches.(and current flowing a different directions during forward and reversing) And to your point of diode being across the limit switch terminals . I don't think it would work as pictured . My thinking is the current would just feed around diode as pictured .But put in lined before or after limit switch it would work ? (not sure if it has to be before or after limit switch to work) Don't think that part matters. Look in the link I posted here under technical drawings.

    https://www.firgelliauto.com/products/external-limit-switch-kit-for-actuators
     
  5. crutschow

    Expert

    Mar 14, 2008
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    You are right about the diode being wired across each limit switch so that the forward current is stopped through the limit switch when it opens but the reverse current can flow. I missed that.
    In that case the diodes have to carry the whole actuator current.
    And no, you don't want the diodes in series with the switch, you want them in parallel but in reverse direction to the current direction when the actuator is moving towards that NC limit switch..

    The circuit I showed is for suppressing the inductive kick of the actuator, which could damage the contacts, and would be in addition to the diodes across the switches.
     
    Last edited: Dec 25, 2015
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